# PSAT Math : How to find the amount of sales tax

## Example Questions

### Example Question #1 : How To Find The Amount Of Sales Tax

If there is a 10% sale on an item, and then 9% sales tax is applied to that after-sale price, then what is the total cost of the item including tax as a percentage of its pre-sale sticker price?

98.1%

99%

101%

99.2%

81.9%

98.1%

Explanation:

A 10% sale means that the post-sale price of the item is now 90%, or 0.9 of the original cost of the item. We then apply 9% sales tax by multiplying the 0.9 by 109%, or 1.09. 0.9 * 1.09 = .981, so the total cost of the item is 98.1% of the original pre-sale sticker price.

For percentage problems that do not deal with a specific starting number, it is always helpful to plug in 100 for the starting number. Here, we would then have a post-sale price of 90 dollars, and if we calculate the sales tax for the 90-dollar item it would be 90 * 0.09 = $8.10. THis gives us a total cost of 90 + 8.10 =$98.10, or 98.1% of the original 100-dollar price.

### Example Question #1 : How To Find The Amount Of Sales Tax

Cynthia buys 2 shirts, each costing $35, a pair of pants for$40 and a belt for $18. At the register the total she owes is$138.24.  What is the rate of sales tax in her state?

Explanation:

To find the amount of sales tax, take the difference in the total before and after tax  and divide by the price before tax.  This gives 0.08 or 8%.